The invention relates generally to medical fluid flow valves and more particularly, to valves that automatically shut off when fluid reaches a certain level.
During hospitalization, a physician may desire to infuse a medical fluid into a patient's bloodstream. The medical fluid may be for therapy, the replacement of body fluid, or for other purposes. During the administration of medical fluids to a patient, it is important to avoid the infusion of air in amounts exceeding a certain quantity threshold. If too large a quantity of air is allowed to enter the patient's blood stream, an embolism could result, which can be a serious condition.
In infusing medical fluids, many times a medical fluid reservoir, such as a bag or bottle, is hung in an inverted position and its contents are allowed to infuse into the patient either through gravity or with the aid of an infusion pump that accurately controls the flow rate in accordance with programmed instructions. A fluid administration set is used to conduct the fluid from the bag to the patient and comprises a fluid line that is connected to the inverted bag at one end, referred to as its proximal end or upstream end, and is connected to a catheter inserted into the vein of a patient at the other end, referred to as its distal end or downstream end.
Many fluid infusion administration sets include a device known as a drip chamber. This device may include a sharpened spike at its upstream end for penetrating the stopper or septum of the reservoir, which may take the form of an inverted bag, bottle, or other type of container, to gain access to the contents of that container. The spike has a length that extends into the fluid of the reservoir and consequently conducts the contents of the reservoir to a precise drop former located at its inlet or upstream end of the drip chamber. The drop former forms drops having a known quantity of liquid that fall to the downstream end of the drip chamber due to gravity. The drops may be counted per unit of time to determine the flow rate of fluid into the patient. The drop former is located within the chamber of the drip chamber and at the downstream end of the chamber, in which the formed drops fall or “drip,” an outlet exists that connects to the tubing of the administration set. That tubing provides a conduit for the medical fluid to flow to the patient.
Nurses monitor the drip chamber for the presence of drops to be sure that the medical fluid reservoir has not emptied. As is well known to those skilled in the art, drip chambers are designed to continuously have a certain level of fluid within the chamber when the flow of fluid into the patient is proceeding normally, such as 3 ml. When the fluid in the reservoir and tube above the drip chamber is exhausted and drops cease to fall, the level of fluid in the drip chamber will decrease until eventually it is empty. Unless the administration set tubing is clamped or other action is taken, air may then enter the administration tubing to which the drip chamber is connected. Thus, an empty fluid reservoir may result in air being drawn into the drip chamber and tubing and consequently being infused into the patient unless the line is clamped or other action is taken.
Additionally, if the fluid level in the drip chamber is permitted to decrease too far, the nurse cannot replace the empty fluid reservoir with a full reservoir unless the entire administration set is primed again to remove air that has found its way into the line. Priming the line takes time and it is desirable to provide devices that control the entry of air into the fluid line so that the procedure of re-priming is not necessary. In particular, it is desirable that enough fluid remain in the drip chamber when the present reservoir is exhausted so that a new fluid reservoir may be connected to the drip chamber and the flow of new fluid to the patient begin without the need for re-priming the fluid administration set.
In another application, the drip chamber may form a part of a burette and be located at the distal, or downstream, end of the burette chamber. In such a case, the drip chamber would not include a sharpened spike but would include the other elements discussed above. In yet a further arrangement, the drip chamber may not have a spike but may instead be fed at its upstream end by a length of tubing that has an integral spike for establishing communication with the container of medical fluid. The spike on the tubing is inserted into the reservoir and the fluid flows through the short length of tubing into the drip chamber.
It is desirable to provide a device that automatically shuts off flow when the medical fluid reservoir becomes depleted. Therefore, those in the development of medical fluid infusion devices have created various shut off valves that have been incorporated directly into the drip chamber device to automatically shut off fluid flow through the fluid line once the medical fluid reservoir has emptied. Some of these systems are relatively complex while some are simpler. One class of such devices uses a device that floats in the liquid of the drip chamber and has a valve seat located at the downstream end of the drip chamber. As is typical in these designs, the floating device floats at a certain level in the fluid dependent upon the buoyancy of the floating device. The floating device is designed to seat when the fluid in the chamber decreases to a certain low level. As the level decreases, the float approaches nearer and nearer the valve seat until it finally seats and shuts off flow thereby providing an automatic shut off valve that does not require constant monitoring.
Problems have arisen with such devices, one of which is that the floating device may not properly seat and completely shut off flow. Under adverse conditions, such as where the administration set may be moving from side to side or oriented at an angle other than directly vertical, the valve device may be slow in seating and fluid shut off may be delayed, thus raising the possibility that air may enter the administration line. Another adverse condition that arises is when a pump operating at a low flow rate is engaged with the fluid line and is creating pulses in the fluid upstream that tend to bounce the floating device away from the valve seat. These pulses may be strong enough to overcome the gravitational force on the floating device and it may not seat when desired.
A variation in this type of automatic shut off valves has incorporated magnetic force to assist in fluid line shut off. The force of magnetic attraction is used between a float located in the drip chamber and a stationary part, such as a valve seat, to shut off fluid flow in the administration line. Such an approach has an advantage in that it acts as a latching-type of valve. That is, the magnetic field or fields used have a field strength that increases non-linearly as the distance between the magnetic devices decreases. While some attraction exists when the magnetic devices are relatively far apart from each other, that attraction increases as they near each other until finally, the magnetic force provided by their attraction overcomes the buoyancy of the float in the drip chamber and it is drawn into a seating position in this magnetically activated valve thus positively shutting off fluid flow.
This magnetic force developed between the two parts tends to hold the valve in the closed or shut off position better than other valves that rely only on gravity. Where prior floats relied only on their weight to seal the fluid line, the use of a magnetic force as well as the weight of the float result in a better chance that the float will completely seal and shut off flow before air enters the fluid line. The use of a magnetic force also tends to draw the float into the seat when the drip chamber is tilted out of vertical alignment. Once seated, the valve is “latched” in that some mechanical force beyond that provided by the mere buoyancy of the float developed by newly added fluid is required to separate the float from its valve seat. Even filling the drip chamber with fluid will typically not dislodge the float from the valve seat in these devices. The force of the magnetic attraction to the seat exceeds the force provided by the buoyancy of the float and some mechanical force is necessary to dislodge the two. Typically, the wall of the drip chamber needs to be squeezed to dislodge the float from the valve seat so that it may rise to the level of the fluid.
While the use of magnetism in drip chambers has been an improvement in the art, certain magnetic devices have drawbacks. Magnetic devices comprising metallic elements should not be exposed to medical fluid in the infusion line. Additionally, some prior devices have uniquely shaped float devices that must be installed in a particular orientation in the drip chamber as the device is manufactured. Failure to properly orient the parts during manufacture can result in a valve that does not completely seal and may therefore need to be scrapped. Such requirements increase manufacturing costs. In other devices, the seal is formed between relatively rigid surfaces, and this configuration may give rise to the problem of leakage at the seal due to imperfections, or lack of fit, between the sealing surfaces. In yet another arrangement, the two devices comprising the valve, at least one of which is a magnet, may not be aligned so that the lines of magnetic flux between the two devices are then not optimally effective. In such a case, a larger magnet is used, which can increase costs. Magnetic shutoff valve devices are further subject to other troubles. The valvets emission of a magnetic field may negatively affect things such as whole blood containing iron. Also, strong external magnetic fields may influence the valve seal, either causing premature occlusion or preventing sealing when it is needed. Moreover, a magnetic shutoff valve device would not be suitable in an MRI environment, thus limiting its range of applications.
Hence, a need has been recognized by those skilled in the art for an automatic shut off valve usable in fluid administration lines that is efficient and reliable in operation. A need has also been recognized for an improved automatic fluid shut off valve that uses an attractive force between valve elements to result in a more dependable shut off action of the valve yet, does not interfere with the components of medical fluids, blood, or an MRI environment, or other medical environment. Yet a further need has been recognized for a fluid shut off valve that is relatively easy to manufacture and has lower manufacturing costs. The present invention fulfills such needs and others.